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Discussion Starter · #1 · (Edited)
Dear all,

I am currently working in basic 2D CAD to design a new frame for myself. I have been talking to Pinion about the gearbox aspect and to R53 Engineering about the Bos shock.

Now in reference to the design R53 sent this for my design

All the BOS forks come with a standard setting + different spring rates to suit rider weight.

For the rear shock, unlike the competition BOS tunes each setting to the frame, so after the frame is designed we take the motion ratio and calculate the damping force required, along with a spring choice to suit the rider's weight.

So when you have finalized the design, if you could let us have the motion ratio we can work out the optimum damper setting to suit your frame.

The Stoy shocks come in eye to eye lengths 200,216,222,240 & 267mm

The other to consider is the mounting kit, the needle roller bearing requires a 8mm fixing.

Let me know how you get on.
I am planning on using the needle roller bearings but that is minor. What I am unclear about is the details on calculating the Motion ratio. I know I am using a shock length of 222mm eye to eye and I am wanting to produce 195mm vertical wheel travel. How do I work the next step?

The frame is going to be steel. I am also currently looking for a good Tig Welder with all the required gear and my budget is around £1000

Any help and info to what I am looking at would be most appreciated.

Sorry for the question. It is probably something simple but I am unable to decipher as I am currently working on the linkage design. I need to buy linkage unless anyone else is able to provide me with the link data?

Edit: OK just brought linkage and put the details into the system. Is there anyone here who can help me and explain what it shows and what I need to improve. I will send the file over to anyone who is interested.
 

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Basically, the suspension travel divided by the shock stroke (i2i doesn't tell us much) gives you your leverage ratio. You can work that formula to determine any of the unkowns.

Using those same numbers and the rider weight, you can also roughly calculate the spring rate (remember, spring rates are calculated by how much force it takes to compress it one inch).
 

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Discussion Starter · #3 ·
Cheers for th information. When Chris refered it to Motion ratio I wasn't sure what he ment but since it is the leverage ratio it is all easier to know what he requires. I have used linkage to produce the leverage ratio.

The basic terms in what I see leverage ratio is for instance

1st inch stroke = 3.5" wheel travel
2nd inch stroke = 2.5" wheel travel
3rd inch stroke = 2" wheel travel

Total stroke length 3" = Total wheel travel 8"

Average Leverage ratio = 2.6:1 but rate at first inch is 3.5:1, rate at second inch 2.5:1 and rate at third inch is 2:1.

The graph that is produced by linkage shows travel along the X axis from 0 to 195mm and a(mm/mm) from 1.4 to to 2.1. How does this relate to the above ratio? Is this showing for example the wheel travel 25mm has a leverage ratio of 2 and at 100mm has a leverage ratio of 1.75 and at 195mm the leverage ratio is at 1.4?

 

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Discussion Starter · #7 ·
The reason for this is to keep the system simple for single speed and gearbox solution. The system will as you say create allot of drive squat but I am used to this from riding my Commencal Absolut SX which I have been fine riding anything from 20 mile XC loops to full DH runs.

If I move the pivot higher then I need to change the design to allow for a jackshaft system while keeping the shock in the optimum position along with the gearbox, this will keep the single speed chain in place. The rear hub will be a custom single speed fixie as the free wheel is built into the gearbox.

With all the above something had to be sacrificed in the design. Unfortunately at this time I cannot create a design that allows for all the positives without a negative.

I am also trying to keep the weight down as much as possible too. The design based on steel construction for frame is 8.8lbs. I should be looking at around 38.5lbs for complete build including gearbox.

Any input on this is more than welcome but until I can work a new solution to this issue it is the one that will remain.
 

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Discussion Starter · #9 ·
Yes Pinion as in Pinion gearbox. But no they are not selling individual units. I am in discussions with them at the moment. Only on the first stage at this time and R53 have been very good working with me to get the optimum performance out of the Bos suspension.

I am hoping to work on this over the next few months and get the first proto sorted by January. There are going to be 6 proto's built. 2 are then going to be heading over to America and I am talking to someone else about sending 2 to Australia.

With this in mind, the drawing you can see on the front triangle for the data is the 2011 Trek model. As said if anyone has any input. Ideas on how to design the frame to suit a high pivot design instead of concentric while using the gearbox I am all up for that.
 
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